The Art of Manliness brings up an often hotly debated topic: where did some of our odd slang /euphemisms come from? I have seen some lesser known practices and professions are usually responsible for expressions that are a long look back at whatever they represented. Industries such as railroads or shipping/sailing were once huge, and had a great large effect on life. Another example would be war, certainly a far reaching topic, though now not as prevalent, and a few generations of warfare might even confuse a modern soldier from some old slang.
I think he most interesting of this article was "turning a blind eye":

“To turn a blind eye to” – To refuse to see or recognize something
Credited to the famous British Admiral Horatio Nelson whose naval exploits during the Napoleonic Wars (1803-1815) are the stuff of seafaring legend. Nelson was injured early in his naval career, leaving him completely blind in one eye. During the Battle of Copenhagen in 1801, the fiery Nelson was serving under a much more reserved and cautious Admiral Sir Hyde Parker. With the tide of battle seeming to turn against them, Parker raised the signal flag, ordering retreat at the discretion of the captains. When Nelson was notified by his flag captain of the signal, he replied, “You know, Foley, I have only one eye – I have a right to be blind sometimes.” Calmly raising his telescope to his blind eye and aiming it in the direction of the signal to withdraw, he continued, “I really do not see the signal.” Thus, having turned a blind eye to the signal of retreat, he continued to fight, and within an hour had secured victory.

OR, "a clean slate"

“Start over with a clean slate” – An opportunity to start over without prejudice
During a sailor’s turn on watch, he would record the heading to which they steered the ship on a slate kept near the wheel. At the end of the watch, these headings would be recorded in the ship’s log, and the slate would be wiped clean and given to the new watch guard. Thus, the new watch was given a clean slate.

Very interesting stuff. I would list some of our boat-washing slang, but this is a family site...